(a) Field of the Invention
The present invention relates to a display device and a driving method thereof, and more particularly to an organic light emitting device and a driving method thereof.
(b) Description of the Related Art
A hold type flat panel display such as an organic light emitting device displays fixed images for a predetermined time, for example one frame at a time, irrespective of whether or not the images are still images or part of a motion picture. In case of a motion picture, when displaying a moving object, the object is displayed in consecutive frames at discrete consecutive positions in the motion path. Since the frames quickly follow one another, the object's motion appears continuous.
However, when a user views the moving object on the screen, the user's eyes move continuously along the anticipated path of the object. Consequently, the object appears blurred due to the mismatch between the continuous motion of the user's eyes and the discrete motion of the object on the screen. For example, assuming that the object is displayed at a position A in the first frame and at a position B in the second frame, the user's eyes move during the first frame along the object's expected motion path from position A to position B. However, the object is not actually displayed at their intermediate positions between A and B. As a result, the object appears blurred since the image sensed by the user during the first frame is acquired by the user via integrating the luminance of the pixels in the path from the position A to the position B, that is, by averaging the luminance of the object and the luminance of the background.
The degree of blurring in a hold type display device is proportional to the time that the object is displayed in a fixed position. Therefore, an impulse drive method has been proposed according to which the fixed image is displayed for a predetermined time within one frame and black is displayed for the rest of the frame. However, this method decreases the luminance of the image due to the reduced time of image display. Therefore, it has been proposed to increase the image luminance while the image is displayed. Alternatively, instead of displaying black, it has been proposed to display an intermediate luminance between the current frame and a neighboring frame. However, these techniques increase power consumption and drive complexity.
A pixel of an organic light emitting device includes an organic light emitting element and a thin film transistor (TFT) for driving the organic light emitting element Disadvantageously, the TFT threshold voltage changes with time to impede generation of the desired luminance. Also, if the semiconductor material providing the active areas for the TFTs of different pixels does not have uniform properties across the display device, the luminance output is not uniform across the pixels.
Also, when the voltage at the anode of the organic light emitting element uncontrollably changes, the current flowing to the organic light emitting element may uncontrollably change to undesirably affect the displayed luminance.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art known in this country to a person of ordinary skill in the art.